The present invention relates to an improved process for the production of polyalkyl tetrahydronaphthalenes, particularly 1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene, the latter compound referred to herein as "HMT".
HMT and other alkyl-substituted tetrahydronaphthalenes are of significant importance to the perfumery as well as other industries. By conventional acylation processes, HMT, for example, can be converted to 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene, a well known musk perfume. Because of their clean musk fragrance and ability to retain that fragrance over long periods of time, these HMT derivatives are of great commercial value as synthetic musk perfume substitutes for the expensive, natural musk perfumes of the macrocyclic ketone series. Consequently, various synthetic methods have been proposed for the production of HMT, as well as other related intermediates of HMT useful in the perfumery or other industries.
For example, Wood et al., U.S. Pat. No. 3,856,875 entitled "Process for Producing 1,1,3,4,4,6-Hexamethyl-1,2,3,4-Tetrahydronapthalene [sic] (HMT)," discusses a process for the preparation of HMT wherein an equivalent or excess amount of para-cymene is reacted with a substantially equal molar solution of neohexene (3,3-dimethyl-1-butene) and a tertiary alkyl halide in the presence of an effective amount of an anhydrous aluminum halide catalyst suspended in a reaction-compatible solvent. Although any tertiary alkyl halide can be employed in the disclosed process, tertiary butyl chloride, tertiary amyl chloride and 2,5-dichloro-2,5-dimethylhexane are noted as preferred. The process is described as having a solvent dependency, with the satisfactory solvents being ethylene dichloride, chloroform, methylene dichloride, 1,1,2,2-tetrachloroethane, 1,2-dichloroethylene, 1,2,3-trichloropropane, 1,1,2-trichloroethane, monochlorobenzene, fluorobenzene, ortho-dichlorobenzene, and para-xylene. Numerous solvents are stated to be unsatisfactory for use in the disclosed process, such solvents including nitromethane, benzene, nitrobenzene, para-cymene, n-hexane, 1,2,2-trichloroethylene, carbon tetrachloride, 1,1,1-trichloroethane, carbon disulfide, 1,1,2,2,2-pentachloroethane, 1,2-dichloropropane, 1,1-dichloroethylene, and 1,1-dichloroethane. These unsatisfactory solvents are said to yield substantially poorer results.
Wood, U.S. Pat. No. 3,246,044 entitled "Process for Making 1,1,3,4,4,6-Hexamethyl-1,2,3,4-Tetrahydronaphthalene," discloses a process for preparing HMT which includes reacting an alpha, para-dimethylstyrene derivative such as dimethyl-para-tolyl-carbinyl halide, and neohexene in the presence of a catalyst such as aluminum chloride, aluminum bromide and ferric chloride, or other Friedel-Crafts catalysts, at low temperatures. Suitable solvents are listed as ethylene dichloride or carbon tetrachloride, or other inert chlorinated hydrocarbon solvents. It is noted that other solvents such as nitrobenzene and nitromethane, may be used, but the yield of desired product is indicated as generally being lower when such solvents are employed.
Sato et al., U.S. Pat. No. 4,284,818 entitled "Process for Preparing Hexamethyltetrahydronaphthalenes," describes a process for producing HMT comprising reacting para-cymeme with a 2,3-dimethylbutene using a catalytic amount of anhydrous aluminum halide in the presence of a secondary alkyl halide, tertiary alkyl halide, propargyl halide or allyl halide. It is noted that both the 2,3-dimethyl-1-butene and 2,3-dimethyl-2-butene can be employed as the 2,3-dimethylbutene reagent, however, 2,3-dimethyl-1-butene was said to yield better results. The reaction is generally carried out using a solvent, such solvents including aliphatic hydrocarbons, halogenated aromatic hydrocarbons, and halogenated aliphatic hydrocarbons.
Cobb, U.S. Pat. No. 4,551,573 entitled "Alkylation of Aromatic Compounds," discloses a process for the alkylation of aromatic compounds with olefinic compounds in the presence of a catalyst consisting essentially of aluminum halide and elemental iodine. Examples of aromatic compounds described as suitable for use in the process include para-cymene, and olefinic compounds discussed include 2,3-dimethyl-2-butene, isobutylene and neohexene. A mixture of olefinic compounds can also be employed, in which case it is noted that one of the olefins may function as a sacrificial agent. The products of the alkylation reaction described include indanes and HMT-type compounds.
Japanese Patent Publication SHO 57-40420 discusses a method of making HMT characterized by reacting para-cymene and neohexene in the presence of anhydrous aluminum halide as catalyst. Suitable anhydrous aluminum halides are said to include aluminum chloride. The reaction is generally carried in a solvent, however, it is noted that it is possible to conduct the reaction without any additional solvent using excess para-cymene. Examples of suitable solvents are methylene chloride, ethylene chloride, chloroform and other inactive fatty hydrocarbon halides. Other solvents such as aromatic hydrocarbon halides, fatty hydrocarbons, aromatic hydrocarbons, etc., can be used, but it is noted that the use of such solvents generally lowers the yield of the desired end product.
Kahn, U.S. Pat. No. 3,379,785 entitled "Process for Preparing Polyalkyltetrahydronaphthalenes," relates to a process for preparing polyalkyl tetrahydronaphthalenes, and more specifically, a process for preparing HMT. The process involves the reaction of a substituted styrene and a 2,3-dimethylbutene, said reaction being carried out at elevated temperatures and in the presence of a cation exchange resin. The 2,3-dimethylbutene reactant employed is disclosed as comprising either 2,3-dimethyl-1-butene, 2,3-dimethyl-2-butene, or mixtures thereof. The preferably employed solvent comprises an aromatic hydrocarbon, such as, for example, benzene, toluene, ethylbenzene, or a xylene.
Suzukamo et al., U.S. Pat. No. 4,767,882 entitled "Tetrahydronaphthalene Derivatives and Their Production," discloses a process for preparing a tetrahydronaphthalene derivative in an optically active state which comprises reacting a benzene compound and a pyrocine compound in the presence of a Lewis acid, or, alternatively, reacting the benzene with the pyrocine compound in the presence of an acid catalyst followed by treatment of the resultant product with the Lewis acid.
These prior art processes suffer from various drawbacks, including low conversion of reactants, poor selectivity to the desired products, sluggish reaction rates, unacceptably low temperature requirements, unsafe solvent systems, or oxygen sensitivity. New and/or better processes are needed. The present invention is directed to this important end.